The present invention relates to equipment used in subterranean operations and, in particular, to systems and methods for providing torque support to a multilateral window milling system.
Hydrocarbons can be produced through relatively complex wellbores traversing one or more subterranean formations. Some wellbores can include multilateral wellbores and/or sidetrack wellbores. Multilateral wellbores include one or more lateral wellbores extending from a parent (or main) wellbore. A sidetrack wellbore is a wellbore that is diverted from a first general direction to a second general direction. A sidetrack wellbore can include a main wellbore in a first general direction and a secondary wellbore diverted from the main wellbore in a second general direction. A multilateral wellbore can include one or more windows or casing exits to allow corresponding lateral wellbores to be formed. A sidetrack wellbore can also include a window or casing exit to allow the wellbore to be diverted to the second general direction.
The casing exit for either a multilateral or a sidetrack wellbore can be formed by positioning a casing joint and a whipstock in a casing string at a desired location in the main wellbore. The whipstock is used to deflect one or more mills laterally (or in an alternative orientation) relative to the casing string. The deflected mill(s) penetrates part of the casing joint to form the casing exit in the casing string. Drill bits can be subsequently inserted through the casing exit in order to cut the lateral or secondary wellbore.
The mill(s) used to create the casing exit are part of a milling system that is generally conveyed to the location of the lateral or secondary wellbore with drill string or work string. In extended reach well applications, the torque at the surface is not necessarily the same as the torque experienced downhole by the milling system. As a result, the milling system can experience high torque loads while trying to orient, anchor, locate, retrieve, get unstuck, or maneuver the milling system within the wellbore. Such milling systems are limited in torque transmission because they are typically supported only on one side and, as a result, promote uneven loading and twisting on accompanying milling guide tracks which can lead to failure in milling operations. More robust milling systems are therefore needed.